1. Field of Invention
The present invention relates to an apparatus for cleaning a probe; and more particularly to an apparatus for continuously cleaning a conductance style probe in a steam or hot water boiler during operation in order to control the water level therein.
2. Description of Related Art
Conductance style probes are installed in boilers in order to control the water level in the boiler and to prevent the burner from firing if the water level is too low. When water is below the probe, the probe has low conductance and the probe control unit signals the water feeder or pump to turn on and feed water into the boiler. In addition, the burner is prevented from firing because the water level is too low. If the probe is in water, the conductance is high and the probe control unit signals the water feeder or pump to turn off. In addition, the burner is now allowed to fire, if required. In use, as time passes, a layer of deposits can build up on the tip of the probe. The layer of deposits may eventually affect the conductance characteristics of the probe, and result in false probe readings. The false readings may result in either flooding of the boiler or a dry firing of the boiler. To avoid these problems, it is currently recommended that the probes be cleaned on a routine basis. However, such cleaning is costly because it requires shutdown of the boiler and the downside risk for failure to do so can result in the boiler overheating and/or exploding.
By way of example, FIG. 1(a) shows a hot water boiler generally indicated as 10 that is known in the art including a riser pipe 12 having a tee fitting 14 arranged thereon with a probe control 16 arranged thereon. The probe control 16 has the conductance probe generally indicated as 18 arranged therein and inside the walls 20 of the tee fitting 14, as shown in FIG. 1(c). In operation, the probe control 16 provides an electrical signal to the fluid and senses the conductance signal from the conductance probe 18. In this embodiment, the conductance probe 18 monitors the water flowing through the riser pipe 12.
In comparison, FIG. 1(b) shows a steam or hot water boiler 30 having a container 32 with a probe control 34 arranged on a side wall 32a thereof. The probe control 34 has the conductance probe (not shown) arranged therein and inside the side wall 32a, similar to conductance probe 18 in FIG. 1(c). In this embodiment, the conductance probe (not shown) monitors the water level in the container 32 to make sure a minimum safe water level is maintained therein.
FIGS. 2(a), 2(b) and 2(c) show the conductance probe 18 in FIG. 1(c) in greater detail, which includes a base 50, an assembly rod 52, a ceramic insulator 54, a spring washer 56, screws 56a, 56b and nuts 58. The assembly rod 52 is a conducting element partially wrapped with Teflon 53 for providing an electric insulator between the base 50 and the rod assembly 52, leaving a conducting tip 55 as shown. The operation of the conductance probe 18 in relation to the device 10 or 30 (FIGS. 1(a) and (b) and the probe control 16 is known in the art. By way of example, when installed in a boiler or other suitable device, a wire 57a from a printed circuit board 57 in the probe control 16 (FIG. 1(a) or (b)) is coupled between the nuts 58 and the base 50, and a pair of wires such as 57b are coupled from the screws 56a, 56b to ground. When the probe comes into contact with the fluid, a conductance signal is provided to the PCB 57 via the wire 47a. The conductance probe may also take the form of a capacitive-based probe which is known in the art having a layer of Teflon or other suitable insulator or dielectric material covering the whole tip.
Some other patents known in the art having electrodes and/or probes and devices for cleaning the same to detect parameters include U.S. Pat. Nos. 1,473,060 and 4,668,369, which show electrode cleaners having devices for moving a cleaning device to clean an electrode. For example, in the '060 patent, the electrode cleaning device is a rotating brush powered by a motor. In the '369 patent, the electrode cleaning device is a reciprocating wiper structure powered by an air operated cylinder. Other known patents show various means for cleaning shafts, not electrodes, including U.S. Pat. No. 3,216,485 having a loosely fitting collar member arranged on a rod, which forms part of a heat exchanger, to keep deposits from forming on the rod.
In view of the aforementioned, there is a need in the art for a mechanical self-cleaning conductance probe, especially for use in steam or hot water boilers and other devices for heating fluids.